The present invention relates to wireless local area network (WLAN) access points, WiMAX and other cellular communication base station antennas. Metropolitan area WLAN deployment are developed which is based on wireless backhaul connections between adjacent access points. The backhaul connections operate on a higher frequency range than the mobile access (4.9-5.825 GHz vs. 2.4-2.485 GHz). The WLAN backhaul antenna typically consists of a number of sectors having multiple antennas. A typical number of sectors is between three and six. The construction is a compromise between the cost of antennas and radios and the capacity and operating range.
The sectorized antenna arrays can take advantage of polarization diversity which is good for increasing backhaul link reliability and capacity in urban areas. Commonly dual-polarized antennas are used for the required antennas. The available diversity gains from using space diversity (separate antenna arrays located at least several wavelengths apart) and polarization diversity are essentially equal.
Polarization diversity in backhaul can increase link capacity e.g. through the use of MIMO techniques. A polarization agile access point can use two channels to a single link connection or connect to multiple access points in the same beam using alternate polarizations and/or frequencies. Another possibility is to transmit and receive in alternate polarizations, thus easing hardware design as no duplex filters are needed.
Another possibility to improve reception at the access point or base station is the use of circularly polarized (CP) antennas. This may reduce the number of radios in the access point, and still provide good reception of different polarizations. In comparison to a perfectly matched linear polarization (say, vertical transmit and vertical receive polarization), the CP antenna always exhibits a 3 dB lower gain. But, the polarization mismatch loss is never higher than this and thus a better system performance can be accomplished with arbitrary handheld transmitter polarization orientations.
The sector coverage of dual-polarized patch antenna arrays is typically limited to below 100 degrees. Dipole antennas can be used to reach 120 degree half-power beamwidths, but they require shaped ground planes and more height. Patch antenna arrays with wide horizontal coverage are needed to reduce the number of radios in cost-sensitive access points.
The backhaul connection range is limited by the LOS path loss and antennas need to have a high gain for a decent link span and reliability. High gain is obtained by vertically stacking antenna elements.
The available frequency range of the backhaul connection varies between different standards and countries, and there may be specific bands which need to be covered. For example, the 4.9-5.825 GHz band is divided to many purposes. The available range for wireless backhaul connections in the US is 5.25-5.35 GHz and 5.75-5.825 GHz. Inside the EU, the available range is 5.47-5.725 GHz.
It is difficult to design a dual-polarized single antenna element with a very wide operating bandwidth. The element must typically make compromises between polarizations, e.g. one principal polarization covers the full band and the other just a part of the full band.
Thus, there may be a need for a communication network antenna array, and an antenna arrangement having a wide angular coverage while proving a simple arrangement.